1. Field of the Invention
The subject invention relates to electrode structures, to electrode interconnecting systems, to circuit boards and, more specifically, to methods of providing electrode structures on substrates, to methods of providing circuit boards, to methods of interconnecting first and second electrodes extending on opposite faces of the same substrate, to methods of preparing electrooptical light gate structures, to articles of manufacture including electrodes, and to electrooptical light gate structures.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CRF 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material.
To provide for a solder-less connection between adjacent substrates, it has been proposed to provide a deformable elongate core with a plurality of mutually spaced electrically conducting loops. According to one of these proposals, announced under the trademark Elastomate by AMP Incorporated, of Harrisburg, Pa. 17105, individual parallel lines of metal are plated on a thin flexible film which is wrapped around a soft rod of an elastomer, such as silicone rubber.
When such a connector is compressed between two parallel substrates, it is said to be capable of interconnecting printed or plated corresponding circuit elements or pads on the two adjacent substrates.
A similar deformable connector of rectangular cross-section has been shown by J. Marshall and F. Rode in the article "Solder Bump Interconnected, Multiple Chip, Thick Film Hybrid for 40-Character Alphanumeric LCD Application," in SOLID STATE TECHNOLOGY (January 1979) pp. 87 et seq.
In electrooptical light gate structures and other equipment where stresses would impair output or operation, the proposed deformable connector approach would not be feasible. Also, availability of flexible connectors has not solved the problem of interconnecting electrode arrays which are located on opposite sides or faces of the same substrate. This problem has received considerable attention as a result of efforts to lower the necessary driving voltage and otherwise improve the performance of electrooptical light gates by providing the driving electrode arrays on both sides of the electrooptically active substrate as proposed, for instance, in British Patent Specification No. 1,534,027, by Battelle Memorial Institute, published Nov. 29, 1978.
In principle, one could interconnect such oppositely positioned electrode arrays by depositing electrically conducting crossovers through a mask over the substrate edges, with such mask being aligned with the pads or electrode portions at the particular edge. Such a method, however, would pose great aligning problems, especially in large-scale production. This problem complex is, of course, not limited to the context of light gate structures, but applies to various other circuit board or substrate arrangements wherein distinct electrode arrays on different sides of the same substrate are to be interconnected.
In the electrooptical area, electrode arrays on light gate substrates have frequently been provided by thin film techniques and masking or photolithography and etching. Briefly, this involved a deposition of a thin metal film on the electrooptical substrate and a selective removal of parts of the film, leaving optimally the desired electrode arrays on the substrate. Light gate structures made by these methods, especially in the case of very narrow gates, were burdened by an adverse effect of the edges of the gate on the field distribution resulting in higher field intensities required to open the gate.
In an attempt to overcome this difficulty and to provide for a lowering of the requisite driving voltage, electrodes have been formed by depositing metallization in mechanically machined grooves. Reference may in this respect be had to U.S. Pat. No. 3,873,187, by Robert E. Brooks, proposing to cut grooves through a layer of lanthanum-modified lead zirconate titanate and into a supporting substrate, and to form electrodes by placing wires and conductive paste into these cut grooves. The disadvantage of such an approach is that machining inevitably causes chipping of the edges and of the surface, internal stresses near the cut edges and mechanical weakening of the ferroelectric ceramic substrate or chip due to the notch effect of the cut grooves. Also, mechanical machining approaches typically limit the electrode configuration to straight lines and also limit achievable electrode density.